The present invention generally relates to a ball having an air-permeable elastomeric wall defining a fluid pressurized cavity, or the like that includes as the inflation medium a low permeability gas such as a mixture of air and sulfur hexafluoride (SF.sub.6) where the noise resulting from the use of the above inflation medium is ameliorated by including in the ball cavity an amount of material having a configuration such that it is sufficient to disturb its sonic resonance. The invention has been found especially useful and successful when embodied as an improved tennis ball and will herein be described as such.